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Instruction Manual
IM-106-880C, OI
September 2009
Hazardous Area OCX 8800
3-6
BLOWBACK FEATURE The blowback feature blows instrument air back through the center of the
internal filter and out the sample tube of the probe. This removes built up dirt
and particulate from the internal filter, sample line and any optional in-situ filter
on the end of the sample tube. The blowback feature is normally used in
systems that have heavy particulate in the process stream.
The blowback feature requires the optional blowback hardware to be properly
installed external to the Hazardous Area OCX 8800. See Section 2,
Pneumatic Installation, for details.
A Hazardous Area OCX 8800 shipped from the factory must be configured
before blowback can be implemented. This same process must be performed
any time a replacement card stack is installed.
Configuring Blowback with the Field Communicator - HART
1. Use the 375 Field Communicator or AMS software to access the HART
menu.
2. From the DETAILED SETUP menu, select INPUT/OUTPUT.
3. From the INPUT/OUTPUT menu, select BLOWBACK.
4. From the BLOWBACK, select BlBk Enabled. Select Yes to enable
blowback. Also set the following parameters:
BlBk Intrvl - Length of time between blowback events (60 minutes
recommended).
BlBk Period - Length of time blowback is activated (5 seconds
recommended).
BlBk Purge Time - Length of time after blowback is complete before
oxygem/combustibles readings are considered valid (Set as required by
the application).
5. Manually initiate blowback from DIAG/SERVICE, then BLOW BACK,
When select BLOWBACK.
6. Configuring Blowback with the Field Communicator - Fieldbus
1. Use the 375 Field Communicator or AMS software to access the
Fieldbus menu.
2. From the TRANSDUCER block menu, select Alarm Relay/Blowback.
3. From the Alarm Relay/Blowback menu, select Blowback.
4. From the Blowback menu, select Blowback Enabled. Also set the
following parameters:
Blowback Interval - Length of time between blowback events (60
minutes recommended).
Blowback Period - Length of time blowback is activated (5 seconds
recommended).
Blowback Purge Time - Length of time after blowback is complete
before oxygem/combustibles readings are considered valid (Set as
required by the application).
Initiate Blowback - Initiates a blow back event manually.